Recent research suggests that chronic early life stress may pose serious threats to child well-being and set individuals on pathways towards increased physical and mental health problems in adulthood. In addition to being a key health input across the life course, chronic stress is produced through individuals' responses to their environments and thus reflects the interaction of social contexts with biological processes. Improving population health and reducing health disparities necessitates that we understand these socio-biological interactions, particularly during the early stages of the life course when physiological changes may become biologically embedded. This K01 Mentored Research Scientist Development Award in Population Research application addresses this critical research need by proposing a training plan and research agenda that will build on my sociology, family demography and child health background to become an independent, innovative researcher in the area of social contexts, chronic stress and health during childhood. To achieve this goal, I propose formal training and mentoring in the biology of stress, collection and analysi of stress biomarkers, child development, and multilevel modeling. My highly-qualified team of mentors and advisory committee members come from the fields of sociology, demography, epidemiology, nursing, and psychology, reflecting the need for a multi- disciplinary approach in conducting research that integrates biological and social processes. I will use my training and mentoring in these new areas to answer important research questions about how family contexts are associated with chronic stress in children, and the implications of chronic stress for child health and health disparities in the U.S. In the past four decades, there have been large and pervasive shifts in children's family contexts towards unmarried and unstable parental unions, which are often accompanied by socioeconomic disadvantage. Research suggests that these contexts contribute to child health and development disadvantages and the reproduction of social inequalities across generations. However, there has been little attention to assessing chronic stress as a pathway through which family contexts affect child health. The expected outcome of this project is paradigm-shifting research that incorporates biological mechanisms into our conceptualization and empirical tests of family context effects on child well-being. Importantly, the conclusions will go beyond a comparison of married vs. unmarried mother families to consider diverse family structures and processes as they impact child stress and health. Using multilevel and population-based data will advance our understanding of the influence of larger social contexts (i.e., neighborhoods and social status) on these processes and will provide generalizable results. These are critical next steps in child health, family demography, and stress research that will set the stage for future research and policy development aimed at reducing chronic stress and health disparities in children.